1. Field of the Disclosure
The disclosure generally relates to methods for cleaning a distilling column comprising a metallic packing, and more particularly to methods for distilling sevoflurane.
2. Brief Description of Related Technology
It is well known that industrial equipment is susceptible to corrosion. Corrosion is a problem of particular importance for chemical processing equipment, for example, because corrosion salts can contaminate and/or otherwise negatively affect the purity and/or integrity of desired, isolated end products. Therefore, various strategies have been adopted to reduce and/or mitigate corrosion and the undesirable effects thereof on industrial metallic equipment.
For example, high performance nickel-based alloys which are deemed to be substantially resistant to corrosion can be used to construct the metal components of industrial equipment.
Additionally, periodic cleanings can be performed to remove corrosion salts from industrial metallic equipment. Acidic cleaning solutions are commonly employed to remove scale and rust from industrial process equipment such as boilers and heat exchangers. However, acid is corrosive to the metal components of the equipment. Therefore, as disclosed in U.S. Pat. No. 4,637,899, the acidic cleaning solutions can be formulated to include corrosion inhibitors to minimize the corrosive effect that the acid has on the equipment.
U.S. Patent Publication No. 2009/0275785 discloses removing reactive metal salts from the surface of metallic equipment used in the distillation of sevoflurane by contacting the interior surfaces of the equipment with an aqueous solution of a passivation agent which renders the non-inert surface of a metal, particularly stainless-steel, inert. Passivating involves the spontaneous formation of a chemically inactive film on the surface of metals such as stainless steel via exposure to air or other oxygen-containing environments. Exemplary passivation agents disclosed in U.S. Patent Publication No. 2009/0275785 include citric acid, nitric acid, and a mixture of nitric acid and sodium or potassium dichromate. Each of the foregoing passivation agents involves the utilization of a mild oxidant for the purpose of enhancing the spontaneous formation of the protective passive film.